The present invention relates to a gear housing for an aquatic vessel, said gear housing being adapted to he attached at an attachment site to an underside of a hull of said aquatic vessel. The invention also relates to a breakaway safety system for an aquatic vessel, said breakaway safety system comprising such a gear housing. Finally the invention relates to an aquatic vessel comprising a gear housing and an aquatic vessel comprising a breakaway safety system.
Various types of propeller-driven aquatic vessels, such as yachts, ships or boats, are known. Such vessels comprise at least one hull and at least one propulsion arrangement supported by said hull. The propulsion arrangement comprises an engine assembly providing motive power to a propeller assembly adapted to be submerged in water when the vessel is in operation. The propeller assembly comprises at least one propeller shaft, which is coupled to said engine assembly via a transmission shaft. A propeller mounted on said propeller shaft propels the vessel through the water when the engine is running. The propeller assembly is at least partially accommodated in a gear housing attached to the underside of the hull.
It is known to provide the gear housing with some sort of sacrificial mechanical structure, to protect the propeller assembly in the event of an impact with a submerged object. For example, U.S. Pat. No. 6,966,806 discloses a gear housing provided with a replaceable leading edge portion configured to absorb energy during impact. It is also known to include sacrificial mechanical structures to prevent damage occurring to the hull.
These sacrificial structures are however not adapted to protect vessels equipped with larger and more powerful propulsion arrangements. For example, contemporary yachts are sometimes equipped with two engine assemblies each delivering about 660 kW and sometimes as much as 1000 KW. Such vessels are in an impact situation subject to large forces susceptible to cause considerable damage to the vessels.
It is thus desirable to provide a gear housing which better protects an aquatic vessel in the event of an impact.
It is desirable to provide a breakaway safety system which better protects an aquatic vessel in the event of an impact.
It is desirable to provide an aquatic vessel which is better protected in the event of an impact.
According to an aspect of the present invention, a gear housing for an aquatic vessel is provided, said gear housing being adapted to be attached at an attachment site to an underside of a hull of said aquatic vessel. The gear housing comprises at least one weakened region adapted to yield when said gear housing is rotated at said attachment site following an impact.
A gear housing has a longitudinal direction, a height direction and a width direction and exhibits a first end arranged to face in a forward direction when the vessel is propelled forward, and a second end opposite to said first end, which second end is arranged to face in a backward direction when the vessel is propelled forward. The gear housing further exhibits an upper side adapted to face the hull when the gear housing is attached thereto and a lower side opposite to side upper side, which lower side is adapted to face away from the hull when the gear housing is attached thereto. When the first end of the gear housing collides with a submerged object, the impact will cause the gear housing to rotate around an axis extending in the width direction such that the second end of the gear housing is forced up against the hull. Such a Collision may cause considerable damage to the hull. According to the present invention, this problem is solved by providing the gear housing with at least one weakened region that will yield and collapse before the hull and thus allows the gear housing to rotate without damaging the hull. Moreover, the rotation and collapse of the gear housing leads to a concentration of forces to the attachment site that advantageously causes the gear housing to break away from the hull before it inflicts severe damage thereto. To facilitate the break-away of the gear housing, the gear housing is advantageously but not necessarily attached to said hull via a fracturable member.
The weakened region is advantageously located at the upper side of the gear housing, extending in the longitudinal direction from the second end. However, other locations are conceivable as long as the weakened region allows the impact receiving part of the gear housing to rotate relative the hull without causing severe damage thereto. The weakened region may, for example, be located at the centre of the gear housing as seen in the longitudinal direction, extending from the upper side towards the lower side.
The weakened region may be of any suitable shape, for example triangular or rectangular, and is preferably arranged such that it has a large extent where a large displacement of the gear housing is expected in an impact situation.
Seen in the width direction, a part of the gear housing arranged to collapse at an impact comprises either a single wall or a plurality of walls, and the weakening of the weakened region can, for example, be achieved by providing one or more of said walls with one or more recesses, each defining a zone that is thinner and weaker than the rest of the wall. This solution is advantageous in that such walls are easily created at low production costs. It is also advantageous if the recesses are arranged at a distance from one another, so that areas of high strength extending in a first direction at an angle, and most preferably perpendicular, to the direction of the impact force, remain between said recesses, providing stability to the gear housing. in said first direction. Said areas may, for example, provide stability to the gear housing in the longitudinal direction.
The weakened region may also comprise an area made of a material of lower strength in comparison with the rest of the gear housing. A portion of a gear housing wall may, for example, undergo various treatments, for example heat treatment, that reduce the strength of the wall material. Alternatively, at least one portion of a wall may be replaced with a substitute piece made of a low strength material suitable for thin walls. The gear housing may, for example, be made of bronze and the substitute piece of plastic, aluminum or stainless steel. The substitute piece is easily attached to the gear housing, for example by means of an adhesive or fasteners, such as rivets or screws, or by welding or press fitting. The latter solution is advantageous in that it effectively reduces the strength of the weakened region and in that it also reduces material costs and the total weight of the gear housing. Furthermore, the substitute piece is easily attached to the gear housing in such a way that it does not negatively affect the flow resistance. Most advantageous is if the entire weakened region consists of or comprises only one substitute piece, as this facilitates the mounting procedure.
The weakened region may also comprise a large aperture in the gear solution, which further reduces the strength and total weight of the gear housing. However, this is not a preferred embodiment as such a large aperture detracts from the stability of the gear housing, A reduction of the strength and weight of the gear housing is also achieved with a weakened region comprising one or more hollow portions.
If the weakened region comprises one or more recesses then the recesses are advantageously situated so that they cause minimal flow resistance. Accordingly, if the gear housing comprises a compartment defined by opposite side walls, for example a passageway for exhausts from the engine assembly, then the recesses are advantageously formed in the inside surfaces of said side walls. However, the recesses can also be formed in the outside surfaces of the gear housing, in which case the recesses advantageously are tilled with a low strength material, such as plastic, in order to minimize the flow resistance without substantially increasing the strength of the weakened region.
In some embodiments, the gear housing further comprises a tail region located towards the second end of the gear housing, where said side walls meet to define a region of increased strength. It is therefore advantageous if the above described recesses or substitute piece are extended all the way to the second end. An alternative, simple and inexpensive solution is to provide said tail region with an indication of fracture dividing said tail region into a first and a second part in the height direction, said first part exhibiting an oblique surface facing an oblique surface on said second part such that said first and second parts are adapted to slide past one another in the event of an impact. The indication of fracture could, for example, be a slit or recess in the tail region or a substitute piece made of a low strength material.
The weakened region advantageously consists of or comprises one or more weakenings arranged in a pattern so as to form a more or less continuous weakening when projected on an axis extending in the longitudinal direction of the gear housing, to ensure that the entire weakened region collapses when subjected to an impact force.
According to another aspect of the present invention, a breakaway safety system for an aquatic vessel is provided, said aquatic vessel comprising a hull, and said breakaway safe system comprising a gear housing and a fracturable member for attaching said gear housing to said hull at an attachment site. The gear housing comprises at least one weakened region adapted to yield when said gear housing is rotated at said attachment site following an impact. The consequence of this collapse of the gear housing is a concentration of forces to the fracturable member, which causes the fracturable member to fracture, so that the gear housing falls of the hull without causing considerable damage thereto.
According to another aspect of the present invention, an aquatic vessel comprising such a gear housing or a vessel comprising such a breakaway safety system is provided.